It is difficult to predict the impacts from global climate change due to the dynamic nature of natural systems. In addition, it would be impossible to list all of those predicted impacts in a resource such as this one. Instead, we have highlighted a few that have been well acknowledged and/or are already happening, to illustrate expected changes in decades to come. The potential impacts discussed below may vary in severity and timeframes, depending on success of greenhouse gas (GHG) reduction efforts on a global scale.

Modeling and Predicting Impacts

Current general circulation models (GCM) project temperature increases based mostly on GHG emissions scenarios due to anthropogenic activities. Predicting accurate changes due to climate change is complicated, especially because the Earth is not warming uniformly (asymmetric uncertainties), and because of feedback loops in nature, which tend to alter normal climatic processes. For example, as temperatures rise, currently "stored" methane and carbon dioxide (CO2) may be released from melting permafrost, faster decaying soils, or warmer oceans. Another example of a feedback loop is how global warming will impact the level of humidity in the atmosphere. Scientists predict that warming temperatures will increase humidity. However, since water vapor itself is a GHG, additional humidity will in turn increase the warming that will occur.

Despite the complexity, some impacts are currently happening, while others are expected with some certainty.

Weather

Weather is distinct from climate in that weather refers to what is happening outside on any given day or time, and place. Thunder and lightning, snow, torrential downpours, and heatwaves are all examples of weather. The constant recording of weather information helps to determine the climate of an area. Climate is the average weather in a location over a long period of time. For example, a region that does not get much precipitation over many years is a dry climate.

While some climate impacts are difficult to predict, scientists can predict rather skillfully that an increase in extreme weather events, such as hurricanes, floods, droughts, and heat waves will occur as warmer oceans and higher sea level add more heat and energy to weather systems, putting coastal communities at greater risk of storm surges, especially in the Southeast. When weather events occur, they will occur with greater intensity. Rising temperatures are very likely to be associated with more extreme precipitation and faster evaporation of water, leading to greater frequency of both very wet and very dry conditions. Interestingly, scientists from Purdue University believe that changes in vegetation cover can push a "region toward more or fewer extreme events" depending on the location [1].

Freshwater Resources

Changes in climate will impact the availability and quality of water resources around the world. According to the Intergovernmental Panel on Climate Change (IPCC) (Chapter 3 of the Fourth Assessment Report, 2007 [2]), the main impacts on freshwater resources around the world will be the observed and predicted increases in temperatures and precipitation variability. Floods and water quality problems in many regions will increase. Increased demand from burgeoning human populations that are becoming more affluent will contribute to the strain on decreasing freshwater systems.

Changes in water supply will in turn impact vegetation around the world, particularly forests. According to The First National Assessment of the Potential Impacts of Climate Variability and Change [3], reductions in available water and changes in temperatures may cause forests to shift their ranges northward. If the changes happen slowly, the shifts may occur successfully. However, the changes in climate may cause the shifts to occur too rapidly and many species may not be able to adapt. Other impacts include losses from extreme weather events and other disturbances that will impact forest health and productivity. Droughts can dry up vegetation that animals depend on for food and cause seasonal water supplies to dry up sooner than normal or permanently.

Coastal and low-lying areas are some of the most vulnerable of the Earth's systems, which will be impacted as sea levels rise, especially by saltwater intrusion. Risks to coastal systems also include impacts from significant weather events (e.g., hurricanes), coastal erosion, and stresses from land uses and hydrological changes resulting from increased population growth. Coastal erosion and other stresses will impact nearshore habitats and coastal wetlands for many species, including salmon, waterfowl, shorebirds, forage fish, and their dependents.

Sea Level

The contribution of thermal expansion of ocean water, the melting of land-based ice (ice fields and glaciers), and to a lesser extent melting of the Greenland Ice Sheet and the Antarctic Ice Sheet are causing sea level to rise. Tide gauge measurements and satellite altimetry suggest that sea level has risen worldwide approximately 4.8-8.8 inches (12-22 cm) during the last century [2]. Climate models, satellite data and hydrographic observations demonstrate that sea level is not rising uniformly around the world. Some scientist feel that the recent IPCC projections may be significant underestimates of what might occur, even during this century. Sea level rising results in erosion and land loss. Many coastal zones and communities, mangroves, coastal wetlands, will be lost and/or suffer from saltwater intrusion in sensitive inlands.

Other Oceanic Impacts

Since the beginning of the Industrial Age, the increase in CO2 into the atmosphere has been ameliorated in part due to the oceanic uptake of somewhere close to 585 billion tons of atmospheric carbon. Driven by this exponential increase in the atmosphere, the oceans have taken up an ever-increasing amount of that carbon, with a particularly rapid increase after 1950. A record amount of 2.3 billion metric tons of carbon (3) was absorbed in 2008. Today, the oceans hold about 150 billion tons of carbon— a third more than in the mid-1990s. This uptake of carbon, along with other ramifications is having a deleterious effect on ocean chemistry, biology, circulation patterns, and temperatures.

One serious problem occurs when CO2 mixes with ocean water - it reduces the pH of seawater - otherwise known as ocean acidification. The lower pH results in the reduced availability of carbonate ions that play an important role in the formation of shells in shellfish, coral, and marine plankton. Ocean acidification will have an enormous affect on fundamental ocean processes and adversely impact coral reefs, commercial seafood stocks, and the food chain for finfish and other species. But with overall emissions growing rapidly, the proportion of fossil-fuel emissions absorbed by the oceans since 2000 may have declined by as much as 10 percent. Some climate models have predicted that the oceans appear to be reaching some level of “saturation” in terms of CO2 uptake [4,5]. This does not ameliorate the acidification issue, but does imply that the oceans' may have less ability to soak up excess carbon from the atmosphere at the same historical rate.

Vegetation and Forests

Changes in precipitation and temperature will impact vegetation around the world. In the short-term, a modest amount of warming could actually increase the carbon sequestration and productivity of most forest ecosystems across the U. S. According to The First National Assessment of the Potential Impacts of Climate Variability and Change [3], reductions in available water and changes in temperatures may cause forests to shift their ranges northward. If the changes happen slowly the shifts may occur successfully. However, the changes in climate may cause the shifts to occur too rapidly and many species may not be able to adapt. Other impacts include losses from extreme weather events and other disturbances, such as fires and pests, that will impact forest health and productivity.

Another potential theory called CO2 fertilization has been simulated. In this envisioned scenario, with higher ambient CO2 concentrations in the atmosphere, plants would thrive under future climatic conditions. Then, in the process of photosynthesis, plants convert CO2 into oxygen. Some scientists argue that this could potentially provide a negative feedback on changing CO2 concentrations. Others refute that any hypothesized CO2 fertilization response is unlikely to offset a significant fraction of projected increases in atmospheric CO2 concentration over the next century [6].

Agriculture & Livestock

Globally, moderate warming in mid- to high-latitude ranges, coupled with increased carbon dioxide (i.e., the CO2 fertilization theory) that increases the ability of plants to grow, and with increased rainfall, could have a positive impact on crop yields. However, even a small increase (1 to 2 degrees C) in low latitudes is likely to have a negative impact on most cereal crops. Increases in ozone also have a negative impact on crops. Weeds, diseases, and insect pests do better under warmer conditions, causing increased management challenges for growers.

Crop and livestock production will be impacted due to the increased heat, along with pests, water stress, diseases, and weather extremes or weather events, frequent flooding, saltwater intrusion, and other conditions which will require adaptations [6], possibly by altering cropping and crop management practices and/or location. Two (of the many) aspects of climate change of high concern to scientists and the agricultural community are extreme high temperatures and extreme low moisture conditions. In the future, some crops may need to be grown in areas that are currently too cold to support them.

Livestock will also suffer from extreme weather conditions—particularly heat. In addition, CO2 interferes with the nitrogen and protein content of livestock forage and grazing vegetation.

Human Health

Impacts to humans will also be substantial, from occurrences such as disease, food scarcity, deaths and injuries from natural disasters and weather events, extreme heat, and other affects attributable to global warming. Some researchers believe that some of those impacts are already underway.

Malnutrition is already responsible for 3.5 million deaths worldwide, according to the World Health Organization (WHO) [7]. WHO has identified compromised food security as a result of increases in severe droughts and floods as one of five major threats to human health from global warming.

More flooding and other natural disasters may result in deaths and injuries. Flooding can also result in increases in outbreaks of diseases such as cholera, particularly when sanitation systems break down. Over the period of 1995-2004, a total of 2,500 million people were affected by disasters, with losses of 890,000 dead and costs of US $570 billion. Most disasters (75 percent) are related to weather extremes that climate change is expected to exacerbate, according to the Climate Institute [8].

The WHO is concerned about the increase in vector- or rodent-borne illnesses, such as malaria, yellow fever, and dengue. Weather affects vector population dynamics and disease transmission, with higher temperature and humidity considered to be key variables in increased transmission. The distribution of the incidence of vector-borne diseases is grossly disproportionate, with much higher rates in developing countries located in tropical and subtropical areas.

Heatwaves, particular in “heat islands” of urban areas, can directly increase mortality rates, particularly in the elderly or those with respiratory disease. Higher temperatures and the increase in ground-level ozone will hasten the production of pollen in plants affecting those with allergies and asthma.

Fish and Wildlife

Survival of abundant and diverse fish and wildlife populations depend on healthy habitats. Those habitats, on a global scale, are being impacted by climate change. Ideal habitat conditions include suitable water conditions—fresh water for upland species and cold water for salmonids, for instance; the right temperatures; food sources to meet their needs during the different times of their life cycles; and places where they can safely raise their young. As many as 30 percent of plant and animal species alive today risk extinction by 2050 if average temperatures rise more than 2 to 11.5 degrees F (1.1 to 6.4 degrees C) [9]. Recent estimates indicate that 25 percent (~1,125 species) of the world’s mammals and 12 percent (~1,150 species) of birds are at a significant risk of global extinction [10].
Those species with low population sizes and/or specialized habitat requirements will fare worse than other populations.

One of the most troubling impacts is that migrations of many species become out of sync with the food sources that they depend on during their migration. The concern about the timing of phonological events goes beyond migration and may also include timing of blooming, insect hatching, nesting, and breeding). Earlier bloom times and birds ranging farther north have been some of the key indicators that climate change is already having an impact on nature. And, as polar ice melts, polar bears must travel longer distances to find ice for hunting seals or risk swimming from shore to ice floes for hunting—all while facing diminished physical condition due to diminished body condition.

Coldwater fish, such as trout and salmon, rely on water temperatures to remain within 50 to 65 degrees F. According to a new study by the Natural Resources Defense Council (NRDC) and Defenders of Wildlife, “Global warming is likely to spur the disappearance of trout and salmon from as much as 18 to 38 percent of their current habitat by the year 2090.”[11]

Small but prolonged rises in sea temperature force coral colonies to expel their food-producing algae, a process known more commonly as bleaching. Some reefs can recover from bleaching over time, many cannot. As reef systems collapse, fish populations plummet—even causing local extinctions.

Some additional impacts on wildlife include -

Warmer spring temperatures may dry up water in prairie potholes in the most significant waterfowl breeding regions on the North American continent.

Reductions in Arctic ice will reduce important birthing and rearing habitat for ribbon seals.

In previous periods of climate change, fish and wildlife species have been able to adapt to changing conditions because they happened gradually over time. The changes occurring in the atmosphere now are happening at a much faster pace than species are able to adapt. Therefore, it is likely that unprecedented numbers of species will suffer declines in populations and/or become extinct.

Ocean acidification is one issue of grave concern and will have an impact on scores of ocean-dwelling species. Oceans are huge carbon sinks that absorb carbon dioxide from the atmosphere. Excess carbon in the atmosphere, however, is causing more carbon uptake in the oceans lowering their ph balance, resulting in the inability of calcifying organisms such as shellfish like mussels and clams to build and maintain their shells.

Some animals will be squeezed into extinction as their suitable habitat declines. Pikas are a good example. American pikas are found in alpine ecosystems throughout the West. These diminutive creatures have adapted to life in terrain that rarely gets above freezing and may die at temperatures in the 70s. Once they move upslope to stay within those temperature requirements, they have nowhere else to go.

Polar bears are drowning and perishing due to changes in sea ice habitat. These changes are reducing platforms for hunting, habitat for mating, and fewer den areas. They must swim further distances, exhausting themselves, sometimes to the point of drowning. Data shows lower cub survival and lower survival rate of the species in general.

Economic Burden

An abundance of studies of the economic costs from past extreme weather events, and predictive economic modeling based on climate scenarios, forebode significant economic losses "of inaction" for many of the aforementioned impacts. Socioeconomically, many of the aforementioned impacts would most affect the world's poorest populations, and economic impacts will be unevenly distributed.

The Pew Environment Group (Pew) conducts analyses with top-tier researchers on key climate topics such as economic and environmental impacts and practical domestic and international policy solutions. A 2010 study by Pew concludes, "The cumulative cost of the melting Arctic in the next 40 years is equivalent to the annual gross domestic products of Germany, Russia, and the United Kingdom combined," and could reach $2.4 trillion (USD). Another report, by
the Center for Integrative Environmental Research (CIER) at the University of Maryland, quantifies many economic impacts associated with global warming [12]. The U.S. EPA has also conducted analyses of economic impacts of federal climate change and energy legislation.

The Western Sustainability and Pollution Prevention Network (WSPPN) is a cooperative alliance of pollution prevention (P2) programs throughout EPA Region 9 (Arizona, California, Hawaii, Nevada, Trust Territories, and Tribal Lands). The network serves as a technical resource for regional P2 issues through researching, consolidating, and disseminating P2 information. WSPPN was established in 1997 and is run as a service provided by The Business Environmental Program (BEP) at the University of Nevada, Reno.